78: 8–4 (2016) 155–166 | www.jurnalteknologi.utm.my | eISSN 2180–3722 |
REDUCING SOAK AIR TEMPERATURE INSIDE A CAR
COMPARTMENT USING VENTILATION FANS
Haslinda Mohamed Kamar*, Nazri Kamsah, Intan Sabariah Sabri,
Md Nor Musa
Faculty of Mechanical Engineering, Universiti Teknologi
Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia.
Article history
Received
1 January 2016
Received in revised form
18 May 2016
Accepted
15 June 2016
*Corresponding author
[email protected]
Graphical Abstract
Abstract
This article presents an investigation on the effects of using ventilation fans on the air
temperature inside a car passenger compartment when the car is parked under the
sun. It was found from a measurement that the air temperature inside the passenger
compartment could raise up to 48°C. Computational fluid dynamics method was
used to develop model of the compartment and carry out flow simulations to predict
the air temperature distribution at 1 pm for two conditions: without ventilation fans
and with ventilation fans. The effects of fan location, number of fans used and fan
airflow velocity were examined. Results of flow simulations show that a 17%
temperature reduction was achieved when two ventilation fans with airflow velocity
of 2.84 m/s were placed at the rear deck. When three fans were used, an additional
3.4% temperature reduction was attained. Placing two ventilation fans at the middle
of the roof also reduced the air temperature by 17%. When four fans were used a
further 4.8% temperature reduction was achieved. Increasing the airflow velocity at
the four fans placed at the roof, from 2.84 m/s to 15.67 m/s, caused only a small
reduction in the air temperature inside the passenger compartment.
Keywords: Soak air temperature; car passenger compartment; CFD simulation;
mechanical ventilation system
Abstrak
Artikel ini membentangkan hasil kajian kesan menggunakan kipas pengudaraan
terhadap suhu udara di dalam ruang penumpang kereta apabila kereta tersebut
diletakkan di bawah sinaran matahari. Hasil pengukuran menunjukkan bahawa suhu
udara di dalam ruang penumpang boleh meningkat sehingga 48°C. Kaedah
bendalir dinamik pengkomputeran telah digunakan untuk membangunkan model
bagi ruang penumpang dan melakukan simulasi aliran untuk meramal taburan suhu
udara pada jam 1 tengahari untuk dua keadaan: tanpa kipas pengudaraan dan
dengan menggunakan kipas pengudaraan. Kesan kedudukan kipas, bilangan kipas
dan halaju aliran udara kipas turut dikaji. Keputusan simulasi aliran menunjukkan
bahawa penurunan suhu sebanyak 17% boleh dicapai apabila dua kipas
pengudaraan dengan halaju aliran 2.84 m/s diletakkan pada bahagian dek
belakang. Apabila tiga kipas digunakan, tambahan 3.4% penurunan suhu diperolehi.
Meletakkan dua kipas pengudaraan di bahagian tengah bumbung juga
mengurangkan suhu udara sebanyak 17%. Apabila empat kipas ditempatkan di atas
bumbung, tambahan 4.8% penurunan suhu diperolehi. Meningkatkan halaju aliran
udara pada empat kipas yang dipasang di bumbung, dari 2.84 m/s kepada 15.67
m/s hanya menghasilkan penurunan suhu yang kecil.
Kata kunci: Suhu udara jemuran; ruang penumpang kereta; simulasi CFD; sistem
pengudaraan mekanikal
© 2016 Penerbit UTM Press. All rights reserved
Jurnal
Teknologi
Full Paper
156 Haslinda Mohamed Kamar et al. / Jurnal Teknologi (Sciences & Engineering) 78: 8–4 (2016) 155–166
1.0 INTRODUCTION
Air-conditioning (AC) system is the major auxiliary load
for a light-weight vehicle [1]. It is designed to meet its
peak cooling load to sufficiently reduce the air
temperature inside the passenger compartment to a
comfortable level after a 'hot soak'. The passenger
compartment experiences the hot soak state when
the vehicle is parked in the open under the sun.
According to [2], during the peak cooling load
condition the AC system extracts approximately 6 kW
of power from the vehicle’s engine. This is equivalent
to a vehicle being driven down the road at 56 km/hr.
Reducing the peak cooling load will lower the
required cooling capacity [1] which indirectly will
reduce the power consumption of the AC system. As
the system is directly driven by the vehicle's engine, a
reduction in its power consumption could lead to a
reduction in the vehicle's fuel consumption [3]. One
way for reducing the peak cooling load is to reduce
the soak temperature inside the passenger
compartment. For every 1°C reduction in the soak air
temperature, there is a potential saving of 4.1% in AC
system power consumption [4]. A mechanical
ventilator has been identified as an efficient method
for reducing the soak temperature inside the
passenger compartment [5, 6].
Several works have been reported on the use of
ventilation for reducing the soak temperature inside
the passenger compartment. Saidur et al. [7]
investigated experimentally the effect of using
mechanical ventilator on soak temperature inside a
passenger compartment. They found that, by
increasing the air flow rate at the mechanical
ventilator, they were able to reduce the soak
temperature inside the passenger compartment
effectively. Bharathan et al. [8] found that natural
ventilation was able to reduce the soak temperature
inside a passenger compartment during parking. Their
study concluded that the use of natural ventilation
method can be as effective as using forced
ventilation (HVAC fans), provided that the inlet air
vent is located at a suitable place. One possible
location for the inlet air vent is at the foot level.
However, this could cause infiltration of moisture and
air contaminants into the compartment, which are
undesirable. Rugh et al. [9] studied the combined
effect of using mechanical ventilator, solar-reflective
glazing and solar-reflective paint on air temperature
inside a passenger compartment. They reported that
the breath air temperature, seat temperature,
windscreen temperature and the instrument panel
surface temperature were reduced by about 12°C,
11°C, 20°C and 17°C, respectively. Huang et al. [10]
used a 3-D computational fluid dynamics (CFD)
simulation to study the effect of utilizing automatic
ventilation system during idling on air temperature
inside a passenger compartment. The ventilation
system will automatically turned 'on' when the air
temperature inside the compartment exceeds the
pre-set temperature value and turned 'off' when it is
below the pre-set value. They found that this strategy
was able to reduce the air temperature inside the
passenger compartment as lower as the outside air
temperature. Dadour et al. [11] developed a
statistical model to predict the compartment air
temperature variations in a parked vehicle using
environmental temperature and radiation data as
input. They showed that the compartment air
temperature can be reduced by 3°C when the driver's
window of the vehicle was lowered by 2.5 cm (natural
ventilation mode). In a study done by Jasni and Nasir
[12] (2012), the usage of solar-powered air ventilator
was found capable of reducing the average air
temperature inside the car compartment by as much
as 3°C.
This paper presents a study on the effects of using
mechanical ventilator fans on the soak air
temperature inside a passenger car compartment
using computational fluid dynamic (CFD) technique.
The goal is to assess the effectiveness of the
mechanical ventilator fans in reducing the soak air
temperature inside the passenger compartment. A
field measurement was conducted to acquire surface
temperatures at various sections of the car envelope
and the air temperature at two locations inside the
passenger compartment. A CFD simulation model
was developed using Fluent 6.3 software. The model
was validated by comparing the air temperatures at
the two locations obtained from the field
measurement with the values predicted by the CFD
simulation. The validated CFD model was then used to
predict temperature distribution inside the passenger
compartment and estimate the average air
temperature value. The effects of fans placement,
number of fans used and outlet air velocity on the
average air temperature inside the car compartment
were also examined.
2.0 METHODOLOGY
In this study, ANSYS Fluent CFD software was used to
develop the model of the actual vehicle and carry
out the flow simulations, employing the RANS
approach, in particular using the k-ε turbulent model.
Since the RANS approach generally uses many
approximations, it is necessary to validate the CFD
model against the real model. For this validation
purposes, accurate experimental data of the air
temperature inside the passenger compartment is
necessary for comparison. Actual temperatures of the
various sections of the car envelope are also needed
for the boundary conditions of the CFD model. Since
these values are not available in any literatures, the
authors performed their own field measurement on
the actual vehicle that was parked in open area and
directly exposed to the sun. However, for validation
purposes, the vehicle was not equipped with any
ventilation fans. Since the engine was not running, the
air inside the passenger compartment was considered
as stagnant. Movement of the air inside the passenger
157 Haslinda Mohamed Kamar et al. / Jurnal Teknologi (Sciences & Engineering) 78: 8–4 (2016) 155–166
compartment was assumed laminar and heat transfer
process was assumed as by natural convection only.
Therefore, for the validation of the CFD model, a
laminar flow solver was used in the simulation.
2.1 Field Measurement for CFD Validation
A field measurement was conducted on an actual
Proton Saga BLM car which has a metallic white body
colour. The car was parked in an open area and
facing the sunrise direction so that the frontal section
of the car was directly exposed to the sunlight as the
sun rises. The field measurement was conducted with
two objectives. The first was to acquire surface
temperatures at selected points on several sections of
the car envelope. These temperatures will be used to
estimate the average temperature on each section.
These average temperatures will be used as the
boundary conditions for the CFD simulations. The
second objective was to estimate the temperature of
the air inside the passenger compartment, at the front
and rear sections. These temperatures will be used for
validating the CFD simulation model. The field
measurement was repeated for three days in
succession and at the same time to ensure the
consistency of the acquired data. During the field
measurements, there were no occupants in the
passenger compartment and the engine of the car
was not running.
A total of twelve type-T thermocouples with an
accuracy of ±1°C were used to measure the
temperatures at designated points on the seats,
dashboard, roof, front windscreen and rear
windscreen. These points are shown schematically in
Figure 1. All thermocouples were connected to a data
acquisition system as shown in Figure 2(b). Additional
two type-T thermocouples were used to measure the
air temperature inside the passenger compartment,
one at the front and the other at the rear section, at a
distance of 280 mm from the roof as shown in Figure
2(c). This is approximately the head level of the
passengers [11, 13, 14, 15]. The data acquisition system
consists of a standard laptop computer furnished with
PicoLog software and TC-08 USB data logger having
an accuracy of ±0.5°C, as illustrated in Figure 2(d). All
thermocouples were calibrated by comparing their
readings against those of a standard thermometer
having an accuracy of ± 0.1°C, in a simple water
heating experiment.
Figure 1 Locations of temperature measurement points on
various sections of the car body
Figure 2 (a) The Proton Saga car, (b) The data acquisition
system, (c) Additional thermocouples to measure air
temperature at the front and rear section of the passenger
compartment, (d) The TC-08 USB data logger
During the field measurements, temperatures were
continuously recorded from 11 am to 3 pm, every 15
minutes time intervals. Using the recorded steady-
state temperature data at 12 pm, 1 pm, 2 pm and 3
pm, the average temperatures of the seats,
dashboard, roof, front windscreen and rear
windscreen sections of the car were determined. The
average temperatures of these sections as obtained
from the field measurement are shown in Table 1. The
local ambient air temperature at these hours was
observed to be around 36°C. The incidence solar
radiation was estimated to be about 1 kW/m2 [16].
(a)
(d) (c)
(b)
158 Haslinda Mohamed Kamar et al. / Jurnal Teknologi (Sciences & Engineering) 78: 8–4 (2016) 155–166
Table 1 Average temperature of various sections of the car
envelop
Location Average temperature (K)
12 pm 1 pm 2 pm 3 pm
Front
windscreen 317.9 321.5 325.5 322.5
Rear
windscreen 314.7 317.4 321.8 321.2
Roof 316.8 320.8 323.8 320.8
Dashboard 332.0 337.7 345.3 339.5
Front seats 319.1 319.1 319.1 319.1
Rear seat 318.4 318.4 318.4 318.4
Bottom 300 300 300 300
2.2 Field Measurement for CFD Validation
A simplified three-dimensional model of the passenger
compartment of the Proton Saga car was constructed
in Fluent 6.3 CFD software based on the actual
dimensions. The length, width and height of the
passenger compartment are 2523 mm, 1080 mm and
1240 mm, respectively, as shown in Figure 3. The CFD
computational domain is bounded by the roof
section, floor section, the side windows, the door
panels, the front windscreen and the rear windscreen.
The two front seats, the rear seat, the dashboard and
the rear deck were incorporated into the CFD model.
The width of a gap between the two front seats is 320
mm. The steering wheel and the clapboard between
front seats were not included into the CFD model for
simplification. Also, all curved surfaces were treated as
flat surfaces. The side windows and door panels were
constructed in vertical orientation so that we could
assume that no radiation incidence will fall on these
surfaces. The windows and door panels were all
treated as solid walls. Four circular holes, each has
diameter of 6 cm, were constructed on a vertical side
of the dashboard facing the front seats. These holes
represent the inlet vents for the cool air of the actual
car.
Figure 3 A simplified CFD model of the car passenger
compartment
The CFD computational domain was meshed using
tetrahedral elements [16, 17] as shown in Figure 4. A
volume meshing option with a skewness of 0.6 was
chosen to enable automatic meshing process of the
computational domain.
To perform the CFD simulations, we used
temperatures as the boundary conditions instead of
heat flux. The temperatures were prescribed on the
various sections of the car envelope as shown in Figure
5. These temperatures represent the average
temperature values obtained from the field
measurement at the time of 1 pm. This time was
chosen because the solar incidence intensity was at
its maximum value [7]. Therefore we assumed that the
temperatures at this time are the highest values
attained by the car envelope.
Figure 4 The meshing of the CFD computational domain
Figure 5 The boundary conditions prescribed on the CFD
model, based on highest temperatures obtained from the
field measurement, at 1 pm
A laminar flow analysis was used in the CFD
simulation since the movement of the air inside the
passenger compartment was only due to density
gradient resulting from temperature variation [7]. The
effects of thermal radiation was neglected to simplify
the CFD analysis. A pressure-based approach with
segregated algorithm was chosen for solving the
governing equations involving natural convection
159 Haslinda Mohamed Kamar et al. / Jurnal Teknologi (Sciences & Engineering) 78: 8–4 (2016) 155–166
phenomenon. The solution procedure for handling the
coupling between pressure and velocity was based
on a Semi-Implicit Method for Pressure-Linked
Equations (SIMPLE) algorithm. A no-slip boundary
condition was specified on the surfaces of the seats,
front dashboard, rear deck, roof, front and rear
windscreens, side panels, windows and bottom
section. This refers to a condition of zero relative
velocity of the air along these solid walls. The thermo-
physical properties of the air inside the passenger
compartment were assumed constant [16, 18, 19].
Convection condition was applied on the surfaces of
the windows, front and rear windscreens and the roof,
with a constant convective heat transfer coefficient
of 15 W/m² °C. The thickness of all the glass sections
was specified as 5 mm while the roof, which was
assumed as opaque wall, is 12 mm thick [17, 20]. The
convection term of the governing equation was
solved by using the second-order upwind difference
method [16, 17, 21]. The CFD simulations were
performed under a steady-state condition in which a
residual criterion for temperature was specified at 10-4
and for energy was at 10-6.
2.2.1 Mesh Sensitivity Test
A mesh sensitivity test was carried out on the CFD
model to ensure that the meshing has negligible
effects on the results of the analysis. First a CFD analysis
was carried out on the model that was meshed with
certain number of coarser elements. Temperature of
the air at the front section of the passenger
compartment was chosen as the monitored
parameter. The CFD simulation was repeated for
several times, each with increasingly larger number of
elements (more refined meshing). The air
temperatures obtained from these CFD simulations
were plotted against the number of elements used in
the model. The plot is shown in Figure 6. Clearly, the air
temperature obtained from the simulation was
significantly affected by the number of elements used
in the meshing of the CFD model. It is seen that when
the number of elements used were 955,437 and
higher, the number of elements has negligible effects
on the air temperature. Therefore, in our CFD model a
meshing with a total number of elements of 955,437
was adopted for all the proceeding simulations.
Figure 6 Plot of air temperature vs. the number of elements
for mesh sensitivity analysis
2.2.2 Results of CFD Model Validation
We carried out the validation of our CFD model by
comparing the air temperature inside the passenger
compartment, at both the front and rear section,
obtained from the CFD analysis with the
corresponding values obtained from the field
measurement. The temperature values from the field
measurement were obtained from 12 pm to 3 pm and
when the car was not furnished with ventilation fans.
The comparison of these temperatures is shown in
Figure 7. It can be seen that the measured air
temperature appears to increase quite steadily from
12 pm to 2 pm. This is due to a greenhouse effect that
can be explained as follows. Thermal energy from the
sun enters the car passenger compartment through
the windscreens and windows. Some of this energy is
absorbed by the seats, the dashboard and the floor.
When these objects release the energy back, not all
of them were transferred out of the compartment.
Some of the released energy is reflected back since
the energy released by these objects is at longer
wavelengths than the sun thermal energy being
transmitted in. This results in a gradual increase in the
temperature of the seats, the dashboard and the air
inside the passenger compartment. The measured air
temperature falls slightly from 2 pm to 3 pm. This could
be due to reduction in the intensity of the sun thermal
radiation that falls on the car envelop during this
period.
Figure 7 Comparison between predicted and measured air
temperature at the front and rear sections of the passenger
compartment
We can also observe from the figure that the
measured air temperature at the frontal section of the
passenger compartment is always higher than that at
the rear section, except at 12 pm where the measured
and predicted air temperatures are nearly the same,
at both the front and rear sections of the
compartment. On average, the difference between
the measured and predicted air temperatures at the
frontal section is about 3.3%, which is acceptable. The
predicted air temperatures at the rear section of the
passenger compartment are similar with the
measured values, at both 12 pm and 1 pm. However,
the predicted temperatures are lower than the
measured values, at both 2 pm and 3 pm. On
160 Haslinda Mohamed Kamar et al. / Jurnal Teknologi (Sciences & Engineering) 78: 8–4 (2016) 155–166
average, the difference between the predicted and
measured average temperature values is about 3%.
Based on the above finding, in our opinion the
simplified CFD model of the car passenger
compartment we developed in this study is validated,
thus can be used in our proceeding analyses. In the
case when the car is not being furnished with any
ventilation fans, the uncertainty of our results is around
3%.
Figure 8 (a) shows the contour of air temperature
distribution inside the passenger compartment at
steady-state condition when the car is not furnished
with ventilation fan. This result is based on the
temperature boundary conditions prescribed on the
model at the time of 1 pm. Figure 8 (b) shows the
temperature contour on a vertical symmetrical plane
that passes in between the front seats. The locations
of the two thermocouples used to measure the air
temperature at the front and rear sections of the
compartment are shown.
As seen from Figure 8, the air closed to the
dashboard surface is at the highest temperature of
333 K (60°C). Away from the dashboard, the
temperature is seen to fall to 323 K (50°C). Below the
dashboard and close to the rear deck the air
temperature varies from 303 K (30°C) to 310 (37°C).
The air closed to the roof and the front windscreen is
seen at 320 K (47°C). A large section of the air inside
the compartment is seen at a temperature of 318 K
(45°C). The two thermocouples used to measure the
air temperature in the front and rear section of the
compartment give similar temperature readings of
318 K (45°C). It was found that the average
temperature of the air inside the passenger
compartment when no ventilation fans were used is
about 321 K (48°C).
(a)
(b)
Figure 8 Contour of air temperature (K) inside the car
passenger compartment based on temperature boundary
conditions at 1 pm: (a) an isometric view, (b) on a
symmetrical plane of the CFD model
2.3 Effects of Using Ventilation Fans
We carried out CFD simulations to investigate the
effects of using ventilation fans on the soak air
temperature inside the passenger compartment
when the car is parked directly under the sun. We
assume that the fans are running continuously during
the entire period when the car is parked. The
ventilation fans will promote a flow of air inside the
compartment. The air is induced from the inlet air
vents on the front of the dashboard and delivered out
from the compartment by the fans. We extend the
CFD analysis by examining the effects of position of
the ventilation fans, the number of fans used and the
magnitude of the air velocity at the fans on the
temperature of the air. The five different cases that we
considered are summarized in Table 2.
Table 2 Summary of the parametric study
Case Fan Position Number of
fans
Air velocity
at the fans,
V (m/s)
1 Rear deck 3 2.84
2 Roof 2 2.84
3 Roof 4 2.84
4 Roof 4 15.67
In case 1 two ventilation fans were placed at the
rear deck of the passenger compartment. The fans
were placed at a distance of 270 mm from the edges
of the deck. Exterior air was assumed to enter the
passenger compartment through the air inlet vents on
the front side of the dashboard. This influx of air is
promoted by the air movement caused by the
ventilation fans. In case 2, three ventilation fans were
placed at the rear deck of the passenger
compartment. They were placed in a straight line
arrangement, 270 mm from one another. In case 3,
two ventilation fans were placed on the roof in a
straight line arrangement along the symmetrical line,
540 mm away from the edges. In case 4, four
ventilation fans were placed at the roof each directly
161 Haslinda Mohamed Kamar et al. / Jurnal Teknologi (Sciences & Engineering) 78: 8–4 (2016) 155–166
above the seats, 190 mm from the roof edges. These
are illustrated schematically in Figure 9 through
Figure 12. Case 5 is similar to case 4 in terms of number
of ventilation fans used and their location. However,
the outlet air velocity was increased from 2.84 m/s (or
20 cfm) to 15.67 m/s (or 110.5 cfm) based on the work
of Saidur et al. [7]. This is to examine the effects of
magnitude of air velocity at the ventilation fans on the
air temperature inside the passenger compartment.
Figure 9 Two ventilation fans at rear deck
Figure 10 Three ventilation fans at rear deck
Figure 11 Two ventilation fans on the roofs
Figure 12 Four ventilation fans at the roof
2.3.1 Computational Procedure
For the CFD simulations with ventilation fans, the
model was meshed using tetrahedral elements 16, 17]
with a total of 955,437 elements. Volume mesh with a
skewness of 0.6 was used. Temperature boundary
conditions similar to those used in the validation model
were employed, as illustrated in Figure 13.
162 Haslinda Mohamed Kamar et al. / Jurnal Teknologi (Sciences & Engineering) 78: 8–4 (2016) 155–166
Figure 13 The temperature, air flow and pressure boundary
conditions prescribed on the CFD computational domain for
turbulent flow analysis
A no-slip condition was applied to all the walls that
form envelop of the passenger compartment. The
ventilation fans were modelled as a circular hole
having a diameter of 6.5 cm [7]. To simulate the air
flow condition inside the computational domain, two
additional boundary conditions were specified. These
are outlet air velocity at the ventilation fan and a zero
gage pressure at the inlet air vents on the front face of
the dashboard. The air flow vector was applied in the
direction normal to the holes representing the
ventilation fans. The magnitude of the air flow velocity
at the ventilation fan for case 1 to case 5 was
specified as 2.84 m/s (or 20 cfm). For case 6, the air
flow velocity at the ventilation fans was set at 15.67
m/s, based on the work of Saidur et al. [7]. The
temperature of the air at the inlets was set at 309 K
(36°C).
Turbulent flow analysis was chosen for the CFD
simulations with ventilation fans. The two equations
standard k-ε turbulence model was used. This flow
model is known to be robust and widely used by many
for flow analyses [22]. The standard k–ε turbulence
model is a semi-empirical model based on transport
equations for the turbulence kinetic energy (k) and
turbulence dissipation rate (ε). The transport equation
model for kinetic energy was derived from the exact
equation, while the transport equation model for
dissipation energy was obtained using physical
reasoning. The flow was assumed as fully turbulent in
the derivation of k-ε model. A turbulent intensity of 10%
was prescribed at the air inlet vents [16, 17] and
turbulent viscosity ratio was also set at 10%. The
turbulent kinetic energy and turbulent dissipation rate
was prescribed as 1 m²/s². A standard wall function
was used in the turbulent flow CFD simulations.
𝜕
𝜕𝑡(𝜌𝑘) +
𝜕
𝜕𝑥𝑖
(𝜌𝑘𝑢𝑖)
=𝜕
𝜕𝑥𝑗[(𝜇 +
𝜇𝑡
𝜎𝑘)
𝜕𝑘
𝜕𝑥𝑗] + 𝐺𝑘 + 𝐺𝑏 − 𝜌𝜀 + 𝑆𝑘
(3.1)
and
𝜕
𝜕𝑡(𝜌𝜀) +
𝜕
𝜕𝑥𝑖
(𝜌𝜀𝑢𝑖) =𝜕
𝜕𝑥𝑗[(𝜇 +
𝜇𝑡
𝜎𝜀)
𝜕𝜀
𝜕𝑥𝑗] + 𝐶1𝜀
𝜀
𝑘(𝐺𝑘 +
𝐶3𝜀𝐺𝑏) − 𝐶2𝜀𝜌𝜀2
𝑘+ 𝑆𝜀 (3.2)
where 𝐺𝑘 represents the generation of turbulence
kinetic energy due to the mean velocity gradients
while 𝐺𝑏 represents the generation of turbulence
kinetic energy due to buoyancy. The 𝐶1𝜀 , 𝐶2𝜀, and
𝐶3𝜀 are constants whereas 𝜎𝑘 and 𝜎𝜀 are the turbulent
Prandtl numbers for k and ε, respectively. 𝑆𝑘 and 𝑆𝜀 are
the user-defined. Default values of the constants
𝐶 were used as follows: 𝐶1𝜀 = 1.44, 𝐶2𝜀 = 1.92 and
𝐶3𝜀 = 0.09.
3.0 RESULTS AND DISCUSSION
The distribution of air temperature inside the
passenger compartment when two ventilation fans
were placed at the rear deck is shown in Figure 14. It
is seen that the air in the rear section of the
compartment is mostly at a temperature of 313 K
(40C). The air temperature in the front section is varies
from 310 K (37C) in front of the dashboard to 315 K
(42C) close to the headrest of the front seats and to
318 K (45C) close to the windscreen. The air close to
the dashboard is at 323 K (50C). Figure (b) shows the
distribution of air temperature on a vertical
symmetrical plane of the passenger compartment.
We can clearly observe that the region of air with
temperature of 313 K (40C) extends from the rear
deck up to the front of the dashboard and close to
the floor. In frontal upper region the air is mostly at a
temperature of 315 K (42C). The air under the
dashboard has the lowest temperature of about 308 K
(35C). We found that the average air temperature
inside the passenger compartment is about 313 K
(40C). This result shows that when two ventilation fans
were placed at the rear deck, the average air
temperature could potentially be reduced by 8.3C
compared with when no ventilation fans were used.
This represents about 17.4 % temperature reduction
which can be considered quite significant.
(a)
163 Haslinda Mohamed Kamar et al. / Jurnal Teknologi (Sciences & Engineering) 78: 8–4 (2016) 155–166
(b)
Figure 14 Distribution of air temperature inside the car
compartment when two ventilation fans were placed at the
rear deck: (a) an isometric view, (b) on a symmetrical plane
Figure 15 shows the air temperature distribution
when three ventilation fans were placed at the rear
deck. Clearly, the region of air having a temperature
of 313 K (40C) is a lot bigger now, covering almost the
entire rear region of the compartment. On the
symmetrical vertical plane we can clearly see that this
region extends from the rear deck to the front of the
dashboard and closed to the windscreen, roof and
the floor. For this case we found that the average air
temperature inside the passenger compartment is
about 311 K (38C). This suggests that the average air
temperature can potentially be reduced further by
placing three ventilation fans on the rear deck instead
of just two. In this case a temperature reduction of
10C was achieved which represents a 20.8%
improvement compared to the case when no
ventilation fans were used.
(a)
(b)
Figure 15 Distribution of air temperature inside the car
compartment when three ventilation fans were placed at
the rear deck: (a) an isometric view, (b) on the symmetrical
plane
Figure 16 shows the air temperature distribution
inside the passenger compartment when two
ventilation fans were placed at the middle of the roof.
The distribution of air temperature appears to have a
nearly similar pattern as that for the previous case. A
large portion of the air at the rear section of the
compartment can be seen at a temperature of 313 K
(40C). This region of air temperature can be clearly
seen on the vertical symmetrical plane of the
compartment. It extends vertically from the roof to the
floor and horizontally from the rear deck to the front of
the dashboard. Close to the windscreen the air is at a
temperature of 315 K (42C) while below the
dashboard the air has the lowest temperature of 303
K (30C). For this case, we found that the average air
temperature is about 313 K (40C). This shows that
when two ventilation fans are placed at the middle of
the roof, the air temperature inside the passenger
compartment can potentially be reduced by 8.3C,
which represents a 17.4 % reduction.
(a)
164 Haslinda Mohamed Kamar et al. / Jurnal Teknologi (Sciences & Engineering) 78: 8–4 (2016) 155–166
(b)
Figure 16 Distribution of air temperature inside the passenger
compartment when two ventilation fans were placed at the
roof: (a) an isometric view, (b) on a symmetrical plane
Figure 17 shows the air temperature distribution
inside the passenger compartment when four
ventilation fans were placed at the roof. As we would
expect the region of air having a temperature of 313
K (40C) gets larger when more ventilation fans are
placed at the roof. This can clearly be seen on the
vertical symmetrical plane of the passenger
compartment in figure (b). As in the previous case, this
region of air extends vertically from the roof to the floor
and horizontally from the rear deck to the vicinity of
the dashboard and the front windscreen. The air
below the dashboard is at lot lower temperature,
varying between 308 K (35C) to 310 K (37C). For this
case we found that the average air temperature
inside the passenger compartment is about 310 K
(37C). This shows that the average air temperature
can potentially be lowered by 10.7C, which
represents a 22.2 % temperature reduction.
(a)
(b)
Figure 17 Distribution of air temperature (in Kelvin) inside the
passenger compartment when four ventilation fans were
placed at the roof: (a) isometric view, (b) on a symmetrical
plane
The results above clearly indicate that the use of
ventilation fans could potentially lower the average
air temperature inside the passenger compartment
when the car was parked in the open space under the
sun. The results also indicate that the placement and
the number of ventilation fans used have
considerable effects on the percent of temperature
reduction that can be attained. In the last case, we
examined the effect of increasing the air velocity at
the ventilation fans from 2.84 m/s to 15.67 m/s, when
four fans are placed at the roof.
Figure 18 shows the air temperature distribution
inside the passenger compartment when four
ventilation fans were placed at the roof in which the
outlet air velocity at each fan was increased from
2.84 m/s to 15.67 m/s. We can see in figure (a) that the
air at the rear section of the compartment is almost
entirely at a temperature of 313 K (40C) while that at
the frontal section including the air below the
dashboard is at a temperature of 310 K (37C). The air
closed to the roof and the front windscreen appears
to be at a temperature of 315 K (42C). On the vertical
symmetrical plane shown in figure (b), we can
observe that the region of air at a temperature of 310
K (37C) extends vertically from the roof to the floor
section and horizontally from the rear deck to the
vicinity of the dashboard. The air in front of the
windscreen appears to be at a temperature of 313 K
(40C) while the air below the dashboard is at 308 K
(35C). We found that for this case the average air
temperature inside the passenger compartment is 309
K (36C). This result shows that the average air
temperature can potentially be lowered by 11.3C
which represents a 23.6 % temperature reduction. This
result shows that increasing the outlet air velocity at
the ventilation fans to 15.67 m/s has only a marginal
affect on the average air temperature inside the
passenger compartment.
165 Haslinda Mohamed Kamar et al. / Jurnal Teknologi (Sciences & Engineering) 78: 8–4 (2016) 155–166
(a)
(b)
Figure 18 Distribution of air temperature (in Kelvin) inside the
passenger compartment when four ventilation fans were
placed at the roof, with air flow velocity of 15.67 m/s: (a)
isometric view, (b) on a symmetrical plane
The results on the use of ventilation fans on the
average air temperature inside the passenger
compartment of the car are summarized in Table 3.
Table 3 Summary of CFD simulation results
4.0 CONCLUSION
In this article, the effects of using the ventilation fans
on the air temperature inside the passenger
compartment of a car parked openly under the sun
at a time of 1 pm were investigated using CFD
method. The effects of fan location, number of the
ventilation fans used and the air velocity at the
ventilation fans on the average air temperature were
also examined. It was found that, from measurement
without the ventilation fans, the air inside the
passenger compartment could rise to 48°C. Result of
the CFD simulation shows that a 17% temperature
reduction is achieved if two ventilation fans with
airflow velocity of 2.84 m/s are placed at the rear
deck. When three fans are installed at the rear deck,
a further temperature reduction of 3.4% can be
attained. Placing two ventilation fans at the middle of
the roof produces 17% temperature reduction in the
compartment. When four fans are placed at the roof,
a further 4.8% temperature reduction is obtained.
Increasing the airflow velocity of the four fans at the
roof, from 2.84 m/s to 15.67 m/s, give only a marginal
reduction in the air temperature inside the passenger
compartment.
Acknowledgement
The authors would like to acknowledge the supports
from Universiti Teknologi Malaysia and fund provided
by the Ministry of Higher Education (MOHE), Malaysia
throughout this study under the FRGS Vot No. 4F645
and to UTM-PROTON Future Drive Laboratory for
providing the authors a necessary assistance to
conduct the field measurements.
References [1] Levinson, R., Pan, H., Ban-Weiss, G., Rosado, P., Paolini, R.
and Akbari, H. 2011. Potential Benefits of Solar Reflective
Car Shells: Cooler Cabins, Fuel Savings and Emission
Reductions. Applied Energy. 88(12): 4343-4357.
[2] Johnson, V.H. 2002. Fuel Used for Vehicle Air-Conditioning:
A State-by-State Thermal Comfort-Based Approach. Fuel.
1: 1957.
[3] Kamar, H.M., Ahmad, R., Kamsah, N.B. and Mustafa, A.F.M.
2013. Artificial Neural Networks for Automotive Air-
Conditioning Systems Performance Prediction. Applied
Thermal Engineering 50(1): 63-70.
[4] Rugh, J.P., Hendricks, T.J. and Koram, K. 2001. Effect of Solar
Reflective Glazing on Ford Explorer Climate Control, Fuel
Economy, and Emissions. In Proceedings of the
International Body Engineering Conference. 2001, October
[5] Farrington, R.B., Anderson, R., Blake, D.M., Burch, S.D.,
Cuddy, M.R., Keyser, M.A. and Rugh, J.P. 1999. Challenges
and Potential Solutions for Reducing Climate Control Loads
in Conventional and Hybrid Electric Vehicles. National
Renewable Energy Laboratory, Golden, CO, USA retrieved
April, 01, 2013, from: www.ott.doe.gov/coolcar/pubs.html.
[6] Farrington, R.B., Brodt, D.L., Burch, S.D. and Keyser, M.A.
1998. Opportunities to Reduce Vehicle Climate Control
Loads. In Proc. 15th Electric Vehicle Symp., Brussels. Sept.
1998.
[7] Saidur, R., Masjuki, H.H. and Hasanuzzaman, M. 2009.
Performance of an Improved Solar Car Ventilator.
International Journal of Mechanical and Materials
Engineering. 4(1): 24-34.
[8] Bharathan, D., Chaney, L., Farrington, R. B., Lustbader, J.,
Keyser, M., and Rugh, J. 2007. An Overview of Vehicle Test
and Analysis from NREL's A/C Fuel Use Reduction Research.
In Vehicle Thermal Management Systems Conf & Exh. 2007
(VTMS-8).
[9] Rugh, J., Chaney, L., Lustbader, J., Meyer, J., Rustagi, M.,
Olson, K. and Kogler, R. 2007. Reduction in Vehicle
Temperatures and Fuel Use from Cabin Ventilation, Solar-
Reflective Paint, and a New Solar-Reflective Glazing. SAE
Technical Paper. 11194: 2007.
166 Haslinda Mohamed Kamar et al. / Jurnal Teknologi (Sciences & Engineering) 78: 8–4 (2016) 155–166
[10] Huang, K.D., Tzeng, S.C., Ma, W.P. and Wu, M.F. 2005.
Intelligent Solar-Powered Automobile-Ventilation System.
Applied Energy. 80(2): 141-154.
[11] Dadour, I.R., Almanjahie, I., Fowkes, N.D., Keady, G. and
Vijayan, K. 2011. Temperature Variations in a Parked
Vehicle. Forensic Science International. 207(1): 205-211.
[12] Jasni, M.A. and Nasir, F.M. 2012. Experimental Comparison
Study of the Passive Methods in Reducing Car Cabin
Interior Temperature. In International Conference on
Mechanical, Automobile and Robotics Engineering
(ICMAR’2012). Penang, Malaysia: 229-233.
[13] Ivanescu, M., Neacsu, C.A. and Tabacu, I. 2010. Studies of
the Thermal Comfort of the Passenger Compartment Using
Numerical Simulation. In 2010 International Congress Motor
Vehicles and Motors, Kragujevac, October 7th-9th, 2010.
MVM2010-026.
[14] Neacsu, C., Ivanescu, M. and Tabacu, I. 2009. The Influence
of the Glass Material on the Car Passenger’s Thermal
Comfort retrieved April, 01, 2013, from:
http://automotive.upit.ro/index_files/ 2009/2009_B_16_.pdf
[15] Neacsu, C.A., Ivanescu, M. and Tabacu, I. 2009. The
Influence of the Solar Radiation on The Interior Temperature
of the Car. In 2009 European Social Fund (ESFA), Bucharest.
[16] Zhang, H., Dai, L., Xu, G., Li, Y., Chen, W. and Tao, W.Q. 2009.
Studies of Air-Flow and Temperature Fields Inside a
Passenger Compartment for Improving Thermal Comfort
and Saving Energy. Part I: Test/Numerical Model and
Validation. Applied Thermal Engineering. 29(10): 2022-2027.
[17] Sevilgen, G. and Kilic M. 2013. Investigation of Transient
Cooling of an Automobile Cabin With a Virtual Manikin
Under Solar Radiation. Thermal Science. 17(2): 397-406.
[18] Aroussi, A., Hassan, A. and Morsi, Y. 2003. Numerical
Simulation of the Airflow over and Heat Transfer Through a
Vehicle Windshield Defrosting and Demisting System. Heat
and Mass Transfer. 39(5-6): 401-405.
[19] Zhang, D. and Weng, P. 2007. Numerical Simulation and
Experiment Research of Air Organization in Air-Conditioned
Passenger Car. In Building Simulation.
[20] Kilic, M. and Sevilgen, G. 2009. Evaluation of Heat Transfer
Characteristics in an Automobile Cabin with a Virtual
Manikin During Heating Period. Numerical Heat Transfer
Part A: Applications. 56 (6): 515-539.
[21] Sevilgen, G. and Kiliç, M. 2010. Transient Numerical Analysis
of Airflow and Heat Transfer in a Vehicle Cabin During
Heating Period. International Journal of Vehicle Design. 52
(1-4): 144-159.
[22] Fluent, I.N.C., 2006. FLUENT 6.3 user’s guide. Fluent
Documentation
.
